A few simple tips can make the life of new mystery authors a little easier and possibly a little more successful. The first is to read: A writer that stops reading stops the flow of ideas and is never really sure which ideas are current and outdated. By continuously reading the ideas keep flowing and the author keeps abreast of what is happening in the field. And this applies to non-fiction as well as fiction; the more information you have the more likely you are to get details right, and a great mystery depends on getting the details right.
Get used to rejection. Rejection is not something to be feared, but embraced. Very few of your stories will be accepted, but you need to plug away regardless of why the rejections pile up. And remember to have fun: No matter what you write or how much you write find ways to have doing it or you will hit more blocks than you should. So read, have fun, and get used to rejection and you should do well as an author!